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What prevents aircraft with a tailcone APU from using tail-mounted airbrakes?
The BAe 146 and Fokker F-28, which are virtually alone among jetliners in lacking thrust reversers, compensate by using large, tail-mounted airbrakes to help slow the aircraft during descent and landing:

(Image by Adrian Pingstone at Wikimedia Commons.)
According to this answer to a previous question about why we don’t see this on more (and bigger) jetliners, the BAe 146 and F-28 are only able to use tail-mounted airbrakes because, unlike most jetliners, they lack an APU in the tailcone:

...Air brakes such as the RJ100 have only upsides, since they influence drag only, not lift. They're not used everywhere because the bit of fuselage where they are mounted usually houses an APU.

(Emphasis added.)
But I don’t see why having an APU in the tailcone would preclude the use of tail-mounted airbrakes; the APU is situated in the middle of the tailcone and exhausts out the tip of the tail,1 while tail-mounted airbrakes are mounted on the sides of the tail and deploy to the left and right:

(Image by dtom_cro at Photobucket.)
As such, having a tailcone APU shouldn’t necessarily preclude having airbrakes on the sides of the tail; in the 146, the space between the airbrakes is basically empty, with only a light truss supporting the rear collision beacon, but it'd be easy to have something more substantial - such as, for instance, an APU-and-other-machinery-housing structure - in between the petals:

What am I missing here?

1: As @ymb1 points out in their comment, the BAe 146 does have an APU, but its APU obviously does not exhaust out the tip of the tail; that statement regarding APU exhaust placement refers to its location in the vast majority of jetliners in general.2
2: That last statement obviously does not apply for jetliners where that real estate is taken up by a full-blown engine (727, Trident, Tu-154, Yak-40, L-1011, Yak-42, etc.).

@ymb1: Oh, is that what that hole is?  Makes my point even pointier, I guess...

Well spotted. Ive edited the original answer.

Yes indeed, it is possible to combine an APU with air brakes at the rear of the fuselage. The defining factor is not the presence of an APU, but that of a T-tail.
Aircraft with a conventional set of stabilisers mounted on the rear of the fuselage cannot use the tail cone for expanding air brakes, as deploying them would distort the airflow over the stabiliser.
Note that all aircraft systems add weight and money, and aircraft manufacturers look very closely at where to save weight and money. Do air brakes weigh and cost less than wing slats necessary when lift dumpers are used for airspeed reduction during landing? Two manufacturers of T-tail aircraft determined that it does, with the added advantage of reduced Angle of Attack during approach.
Thrust reversers aid in decelerating the aircraft after touch-down. The brakes of a large, heavy aircraft need to work disproportionally harder than those of a lighter and smaller aircraft such as the BAe 146 and Fokker 100. Braking efficiency is improved by deploying lift dumpers, and it may make sense to use these as air brakes during approach. Particularly if stabilisers mounted at the rear fuselage take away the obvious place for mounting the air brakes.

There is no technical obstacle to building tail mounted air brakes and APU.
The Fokker 70 has a tail air brake, APU and also thrust reversers and spoilers as seen in this great photo from airliners.net:
Fokker 70 landing in AMS

there could be a technical obstacle, depending on the space available. After all, both the airbrake mechanism and the APU take up space and the tail end of most aircraft isn't known for having a lot of space. I both the F70/100 and Bae146 the APU sits slightly forward of the actual tail end for that reason, if you look at other designs the APU tends to sit further aft.


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When flying in uncontrolled airspace, which ATC frequency should I contact if I have an emergency?
Question 1: If I am flying in uncontrolled airspace and I have an emergency, should I report on 121.5MHz if no ATC is within line of sight communication (which means I cannot hear the ATC and the ATC cannot hear me)?
Question 2:
Which frequency should I use to report the emergency in the following scenario? When the emergency happens, the aircraft is in uncontrolled airspace but near or approaching controlled airspace. There is an ATC station which is in charge of that airspace and the aircraft is within the line of sight of ATC (which means I may hear them), but my onboard radio coverage (the green circle indicated in the picture) cannot reach the ATC station (which means ATC cannot hear me). Should I report on the ATC frequency as maybe some aircraft are flying in the area and can relay the emergency to notify the ATC? Or should I just keep reporting on the common radio frequency like 121.5MHz?

If you are not actively talking to somebody, always switch to 121.5, the nearest ATC facility will be listening to that. If you are already talking to somebody, just keep talking to them.

That should be an answer Ron.

Closely related

Being in uncontrolled airspace doesn't mean that ATC won't be able to hear you. Monitoring of 121.5 is extensive, so there is a very good chance they'll be able to hear you regardless of where you are. If not, they likely won't hear you on any other frequency either.

I'd contact the nearest TRACON ("approach") or ARTCC ("center")

Related: Flying VFR in uncontrolled airspace, what to do if one spots an apparently out-of-control fire on the ground? (Full disclosure: My own question.)

121.5 is not always monitored https://www.reddit.com/r/flying/comments/a68ta5/psain_an_emergency_if_you_are_already_radar/

@StephenS: Not on any other VHF frequency... but that's (one of the reasons) why you also have an HF radio, which you may now tune to 2.182 MHz to report your emergency.

The safest approach is to use 121.5 until someone instructs you to try another frequency.  ATC will monitor 121.5 at all locations it has antennas at. Additionally, military, some airlines, some medvac, and other operations will monitor 121.5  So your coverage will be greatest if you just use 121.5, unless you are already talking to ATC.
Addendum: Really in uncontrolled airspace?    If you are really in uncontrolled airspace, in the CONUS, you are likely flying rather low.  121.5 will be your best best in that case as well.  With enough time, you might work out a relay with higher traffic, perhaps on a center frequency.  But 121.5 remains the go to frequency.

If the ATC does not contact me, but I could hear people communication on the ATC frequency, that means I am within the line of sight communication of some aircrafts, should it be a better way to talk to the ATC frequency rather than 121.5 Mhz？ Maybe the aircrafts could help me to relay the emergency and also some ATC told me not everyone will monitor 121.5 Mhz

Not all aircraft monitor 121.5, but many do.  My understanding is that all radar communications locations, towers and FSS outlets do.  Aircraft can relay, and if you can't raise ATC they will relay.  In CONUS above 5000 AGL it is rare to not reach ATC. In the US all ATC monitor and can communicate on 121.5 unless they have an equipment failure.

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Are we on the "wrong boat" with eliptical spanload all these years?
In this video AL Bowers (former NASA chief scientis) talk how bell spanload solution  can reduce OVERALL DRAG by 60%(11% reduction in total aircraft drag due to spanload, elimination of the tail results in another 20-30% efficiency gain, and then 15.4% improvement in propulsive efficiency, the total efficiency increase is on the order of 60%) and  how today aeronauticals engineers dont understand at all "bell spanload concept".
So are we using "wrong" spanload solution(eliptical or all versions of eliptical) all these years?
sources :
NASA link
on bell spanload(right wing) resultant force is tilted forward, that cause thrust at wingtip. Eliptical spanload(left wing) has drag at wingtip.

often people think,that wingtip produce download(negative lift),this is not true, wingtip produce lift all the time you can see from graph lift dont go below zero line.

I don't know how representative the images are, but the integrated lift on the left side is substantially larger than on the right side. It makes sense that you have less induced drag if there is less lift.

the answer to such questions is almost always a resounding NO when it comes to engineering problems.
There might be room for improvement on existing principles, but that doesn't mean those principles aren't sound if they've been shown to work and work well for a century or more.

what are you trying to optmize for? did the people that came up with the elliptical distribution optmize for the same? did you use the same boundary conditions/constraints?

These are low speed soaring bird designs, yes, they all work well but produce too much drag at higher speeds.  I would question "tail elimination" claims, as loss of stability would greatly increase drag (pitch and yaw oscillations) and hinder low speed control.  Birds kept theirs.

It is misleading and incorrect to presume that a negative AOA at the tip will result in upward lift and forward thrust. I understand how the vortice could be reduced, but the net lift vector will in that section will be downward, not forward and up.  Because if you could generate "induced thrust" in the way it is shown in the diagram on the right, why wouldn't you design a wing with the camber on the bottom to take full advantage of this?  (or camber on the top, but negative AOA?!) It defies common sense...

The elliptical and bell curves give optimal solutions to different problems. Obtaining the most efficient wing for a given span leads to the elliptical distribution, whereas the most efficient wing for a given load is given by the bell distribution. For a given central load, the bell or Prandtl wing will have longer span but a lighter structure and reduced tip losses.
For a swept wing the Prandtl type is inherently stable, so there is no immediate need for a tail stabilizer. However practical considerations include CG range, and this is the tailless type's big weakness: unless it is sharply swept, as in a typical supersonic delta, it will in practice need a separate elevator, fore or aft, to apply the significant trim changes as payloads vary for operational reasons. For a straight wing an airfoil with reflex camber to give a static center of pressure will also make it stable, but such airfoils are relatively inefficient and wing area must be increased.
Also, if a significant fuselage is added to increase payload volume, this is likely to extend forward of the wing and need a compensating vertical fin, despite the inherent stability in the turn of the Prandtl wing through proverse yaw. All this reduces the practical advantage of the Prandtl wing well below its theoretical value.
Roll inertia will also be affected by the increased span, which can impact highly manoeuvrable or very large aircraft.
One way of looking at the Prandtl wing is to see the tip section as a vortex-reducing winglet, which just happens to be blended in. I recall the Airbus A380 chief designer saying that it makes little difference in practice whether the winglet section is horizontal or vertical.
Having said all that, I am a fan of the Prandtl wing (which is really the Dunne-Prandtl wing, as J W Dunne discovered it empirically and flew it as the D.7, twenty years before Prandtl did the maths and a century before Bowers flew the Prandtl-D). Now that NASA have rediscovered it, I would expect it and its design principles to find some modest wider application in the future, with or without a tail. For example in long-endurance electric drones with fixed CG and minimal maneuvring needs.

wingtips at bell spanload are never negatively-loaded,they always produce small lift,look at lift distribution at my diagram,if wingtips have negative litf than lift  will goes below zero line...

Ah, OK, Figure 4 in Bowers' original paper appears to show it, but on checking I see that it is relative to the elliptical loading and not absolute. I'll edit my answer accordingly. Thanks.

Any better now?

@ROTOR It depends. On some designs it can be constantly negatively loaded. In other designs it is less loaded. It also depends on the bell curve. Using Horten bell distribution the wing tips are usually negatively loaded. Using Prandtl bell distribution the wing tips can often be neutrally loaded or even positively loaded. Partly this is caused by the Horten brothers' misinterpretation of what makes the bell-shaped curve stable for flying wings and they didn't fully trust Prandtl's results so made the tips negatively loaded for safety margin.

… and how today aeronauticals engineers dont understand at all "bell spanload concept"

This is another case of NASA marketing overselling their achievements. The engineers of the past understood the concept fully well. Note that even Ludwig Prandtl himself wrote in the article "Über Tragflügel kleinsten induzierten Widerstandes"

Die Abbildung zeigt, daß die in letzter Zeit bevorzugten spitzendigen Flügel von unserem Standpunkt aus den Vorzug verdienen, vor denen mit annähernd rechteckigem Umriß, daß es dabei aber im einzelnen auf den Grad der Zuspitzung nicht allzusehr ankommt.

Translation:

The illustration shows that from our point of view, the recently preferred pointed wings deserve preference over those with an almost rectangular outline, but that the degree of tapering is not too important.

Interpretation: The engineers were already designing wings with something like a bell or near triangular lift distribution. And they continued to do so until recently. Witness the article "The aerodynamic design of the A350 XWB-900 high lift system" by Henning Strüber, where he writes on the first page:

The highly tapered inboard loaded wing is optimized for aerodynamic cruise efficiency and low structural weight.

"inboard loaded" is just another term for a bell-like lift distribution over span. Again, high taper has been used to reduce the root bending moment. And you can rest assured that engineers will continue to design such wings in the future, NASA marketing notwithstanding.
Next, the number of 20 to 30% in savings by leaving off the tail is higher than the tail drag contribution of most designs, so there is less to save to begin with. But tailless designs need much larger wings to create the same lift since part of the wing is needed for stability. Tailless designs cannot use powerful flaps, and only by using large flaps can airliners cover the speed range that makes them so efficient. Al Bowers should know this. The claim of 60% of drag reduction is only possible if one particular operating point of a very poor design is compared to an ideal tailless design. Overall efficiency will be poorer than that of conventional designs.

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Why did Air France flight 447 fail to recover from the stall?
I have read the wikipedia entry about the accident but I don't understand why did the stall happen and why the plane couldn't recover from the stall.
Correct me if I am wrong but I would think a plane would naturally recover from a stall situation by pitching down the noise by itself with no control inputs needed and gaining speed (due to the fall).  The AoA would be back to safe values to generate lift again and the plan would be stabilized.
I don't get how a plane like that would fall from 35,000 feet with its engines set at 100% thrust.

I‘ll attempt a very brief answer based on the report against your questions:
1) Why did the aircraft stall?
The aircraft stalled because crew pitched the aircraft up beyond the performance limit at that altitude (they pitched into a climb which the available engine thrust could not sustain, bleeding off speed until the aircraft stalled).
2) Why was power not reduced?
I don’t know, but in my view that didn’t play a crucial role, either.
3) Why did the aircraft not pitch down by itself?
Because crew didn’t realise they were stalled and continued to apply „nose-up“ control input. Seemingly inconsistent behaviour of the stall warning system and unexpected parameters on their instruments (i.e. a combination of speed and vertical speed not ever seen in normal flight) contributed to the situation.

@lmaxd Without trying to sound bitter or anything, at some point I‘d be interested in some constructive feedback as to why my answer did not work as well as the accepted one - this might help me in future answers.

The accepted answer gave me a better understanding of the physics of why the the plane did not at some point during the (free ?) fall pitch down by itself. I should have put more emphasis on that particular aspect in my question. Thank you.

@Imaxd Fair enough. Didn’t see that particular relevance originally and tried to answer your questions as I understood them. Thanks for commenting!

Thanks for the report.

In the larger sense, the aircraft didn’t recover from the stall because the pilots were confused on what operating mode they were in (mode confusion).
So much functionality has been placed into software, that flying in different modes can literally be like flying different aircraft. The relationship between control inputs and control surface movements can completely change.
In short, they thought they were flying Aircraft X when they were actually flying Aircraft Y. They flew a perfectly operable aircraft into the water because of it.

This ties in with another current question about why we do not have larger elevators on airliners, and highlights the potential of accelerated stalls.
Aircraft need proper air flow over the wing to produce adequate lift.  This is a function not only of speed, but also of angle of attack.  The lift to angle of attack chart illustrates this.
One of the key functions of a properly designed horizontal stabilizer is to push the nose down when the plane sinks.  The design parameter is to have this have adequate area on the H stab to lower the nose as it sinks before it stalls.  The pilot adds power to resume level flight.
The other critical factor is center of gravity.  A forward set CG again pulls the nose down as the plane slows.  Forward set CG acts as a counter balance to elevator trim to stabilize air speed to a desired range: slower - nose down, faster - nose up.
It is the position of the elevator that creates the AOA to stall the aircraft.  If the elevator is stronger than the torques created by Hstab while sinking and forward CG, the plane cannot sufficiently reduce AOA.
Sadly, even with power applied, the stall can not be broken until the elevator is released.  In the report of this incident, although pitch did not exceed 15 degrees relative to the horizon, AOA exceeded 35 degrees even with throttle at TO/GA, and the aircraft was falling at over 10,000 feet per minute.  Weight and balance were within limits.

Thank you ! This answers my question about why the plane did not pitch the nose down by itself (thus reducing the angle of attack and gaining lift back) during the fall. Maybe the engines being at 100% thrust compensated the HStab torque ?

It did not pitch down because full down elevator has to be sustained for a period of time and the right seater was holding full aft stick almost the entire time.  The left seater applied nose down stick several times - he had the right instincts - but he didn't hit the override button on his side stick.  Full aft on one side and full forward on the other is summed by the FBW computers and you get neutral elevator unless the left seater hits override.  Then the left seater gave up on that and they were back to full up elevator.

@JohnK The airplane was in a full stall according to the report. Computer systems preventing stall were inoperative during the accident sequence due to initial disagreement between sensors. Angle of attack was beyond 35° which is much higher than stall angle of attack and much in excess of what flight control computers would allow.

You're right I had a different scenario in mind and didn't go back and review the report.

@Imaxd possibly, if the engines were underslung.  But even at full power, with the elevator full aft, a plane will either loop or stall trying.  Even if it is moving forward at 250 knots, if it is sinking at 125 knots, the AOA will be around 35 degrees even with the nose near the horizon.  The elevator authority is key.  Also, as John K stated, for that particular type of plane, the controls were not linked.

"the AOA will be around 35 degrees even with the nose near the horizon" How is that possible ? Isn't the AOA the angle of nose relative to the horizon ? @RobertDiGiovanni

Looked it up to make sure.  AOA is the angle between the RELATIVE wind and the WING.  So, with vectors draw a perpendicular 250 forward and 125 down.  Check the angle.  The aircraft pitch relative to the horizon, according to the report, did not exceed 15-16 degrees. But the AOA was 35+.  The right seat continued inputs after the left seat took control, without communicating.

Lmaxd, you can fly at zero AOA in a vertical climb, and in fact must be at zero AOA if it is a steady vertical climb.

@Imaxd For zero wind, Flight Path Angle is where it goes (relative to horizon), Pitch Angle is where it points (relative to horizon), and Angle of Attack is between the two. AF447 went down a ~20° slope while pointing up ~15°. This makes AoA ~35° (assuming no wind). This also means for speedy recovery they would have had to put the nose at least 15° below the horizon which takes some guts.

So at 35,000 feet (when they still had a chance) (before their vertical speed got to out of hand) it would have been better to pitch down hard with no power rather than remain at high Pitch Angle and TO/GA power? Seems the real key is to catch it before sink adds to the AOA, especially with very large aircraft.  One writer wrote the B-52 "suffers" from lack of elevator authority.  But that may help to avoid a power on stall fully loaded.  Might look good as an airliner.


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How does an airline decide when to cancel a long haul flight permanently?
BROAD QUESTION WARNING: Obviously the airlines cancel the routes because they are not making money, but would that not have been factored in when they start a route? For example, the current SFO-BLR route seems to be fully booked all the time (a friend flew on it recently), but it would not easily be scrubbed given that Air India is still a government owned airline.
Similarly international airlines would not start new flights to Phoenix because of its proximity to LAX. But there is a sizeable amount of traffic that flows between PHX-LHR (It used to be 2 daily direct flights out of PHX pre COVID)

I’m voting to close this question because it appears to be more about travel than aviation.

It depends on whether you are thinking like a passenger, or thinking like an airline exec.  With an “operations” tag it is entirely relevant to this forum.  I don’t think the wording of the question is that great, but it’s in the top 50% of most questions here.  And Dave’s excellent answer bears witness to that.  I’m voting to reopen.

It's really more of an Economics question.

There are various reasons airlines may chose to stop flying a route. While its often financial there are usually underlying reasons that drive the decision. While financial models are drawn up when planning routes, outside factors may effect the finances in unpredictable ways.
Lack of travel: if a destination becomes unpopular or a city sees diminishing travel an airline may chose to stop flying the route, this may come after various scale backs.
Airframes get decommissioned: The economics of a route are often tied to the airframe used to fly it. Historically with the hub and spoke model smaller short range aircraft were used on quick routes. As airlines decommission old airframes some shorter (or even longer) routes are no longer financially viable.
Geopolitical reasons take hold: Its possible for government actions (generally related to visas and passports) to adversely affect travel and thus make a route either not profitable or completely not viable.
Changing Model: This ties into the airframe issues but over time airlines have changed how they approach travel, both as a company decision as well as a response to technological changes in the industry.
"Can't Land here": Sometimes you just can't get the plane in there
Airport Closures: Airports are by no means everlasting, they do sometimes close down
Bigger, Faster, Farther: There are lots of airports scattered all over the globe that acted as common re-fuel spots during the heyday of the large prop planes and were ultimately not needed during the jet age. While some of them remain as emergency landing spots they dont see nearly the traffic they once did and long distance routes simply bypass them.


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Why building a stopway instead of just building a longer runway?
I don't get the point of building a stopway. If you have the space to build a stopway, you could just extend the length of the runway.
Why are stopways necessary?

I sometimes wish we lived on a flat earth where the landscape extends to infinity and real estate would be cheaper.

The question is answered in detail here

@user3528438 Flat Earth is not required to build very long, straight roads. Proof: most highways in non-mountainous parts of the American West. Of course, the road will still follow the curvature of the Earth rather than being literally straight in all three dimensions, but that's not problematic (roads do this anyway, it just isn't very noticeable because the curvature itself isn't very noticeable from the surface.)

Overrun areas are almost always filled with some form of loose material... sand, for example... that will slow a plane down with extra drag on the landing gear. The idea is that if a plane has reached the end of the runway, it's already in trouble and is probably having problems braking.

Ah that already makes more sense. My textbook isn't very clear.

Regardless of how long a runway is built, a stopway is needed for other purposes. Stopways (also known as blast pads or overrun areas) is often not as strong as runways, so that airplane's tires have more friction and can slow down faster than runways. Also, the length of a runway does not include the length of stopway.
Why runways are not built longer? It is because real estate is real estate. It is expensive and is always on short supply. Also, if you find area around a runway which is not used, there could be rules for that region for open space.

Also, even if you have plenty of real estate, runway construction is decidedly not free.

Stopways are different from blast pads, as blast pads are not intended to support the weight of an aircraft. See page 3-22 of https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/1040834

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How to calculate Blade angle?
If we know the helix angle is 3angle, forward speed is 150mph, and rotational speed of propeller is 1500rpm
How can i calculate the blade angle of propeller ?

What do you mean by 3angle?

In case you want to know at what angle does the blade 'see' the incoming wind, you first choose an station of the prop, say at 70% of the prop radius, measured from the axis. If the prop has a radius of 1,2 meters, that station is at a distance 1,2 x 0,7 = 0,84 meters from the axis. Let's imagine, to start with, that the plane is stationary, and the prop turns at 1500 rpm. That's 25 revs per second. In every revolution, our station moves a distance of 2 x π x 0,84 = 5,27 meters. Thus, the chosen station sees the wind coming parallel to the plane of rotation, at an speed of 5,27 x 25 = 131,75 m/s.
But if the plane is moving forward at 150 mph, that's a frontal airspeed of 67,04 m/s. That additional, frontal wind is 'seen' by the station as coming from 90º to the plane of rotation. If you now draw the triangle of velocities, you have one side measuring 131,75 and the other 67,04. The angle (with the plane of rotation) of the total relative wind obtained by (vectorially) adding the two winds is arc tan 67,04/131,75 = 27º
Hope that helps...

Some formatting would really help this answer.

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Why can’t air traffic control radars determine the altitudes of primary targets?
There are two types of returns that show up on an air traffic controller’s radar screen:

Secondary returns are not, strictly-speaking, radar “returns” at all, but, rather, signals automatically broadcast from an aircraft’s transponder, containing encoded location, altitude, airspeed, identification, flightplan, aircraft type, etc., data retrieved from the aircraft’s onboard instruments.  These are highly valuable, but, obviously, can only be used with aircraft equipped with a functional transponder which have said transponder turned on and transmitting non-bogus data.
Primary returns, in contrast, are true radar returns – direct reflections of the radar’s beam from the surface of an aircraft, bird, cloud, piece of debris, missile, tree, UFO, balloon, hailstone, or whatever else happens to be in the air at that moment.  As they merely require that an object be located where the radar beam can reach it, they are of great use in tracking aircraft with nonfunctional transponders (due to, for instance, a general electrical failure or simply a faulty transponder), aircraft in combat zones (for whom broadcasting an identification signal would be a great way to get shot down), pieces of aircraft, flocks of birds, or whatever other non-transponder-equipped objects one has a desire to track.

One common limitation given for primary radar returns is that they provide no altitude information, but only positional information.  But this makes no sense, as determining the position of a target requires knowing its elevation angle, azimuth, and distance relative to the radar installation (without knowing the target’s distance, it could be located anywhere along a line extending from the radar’s location out to infinity; without knowing its elevation angle, it could be located [within the altitude limitations of the object generating the target] anywhere along a circular arc extending from the horizon to the zenith at the specified distance from the radar; without knowing its azimuth, it could be located anywhere along a horizontal circle centered in the sky directly above the radar), and, if the elevation angle, azimuth, and distance of the target are all known, that also pins down the target’s altitude – not just its location.  Besides, military radars can and do provide altitude information for primary targets (they would be useless otherwise, as intercepting an enemy aircraft requires knowing both its position and its altitude, and enemy aircraft are unlikely to oblige a radar’s request to provide a transponder beacon signal that would aid immensely in shooting them down), which has proven valuable numerous times; for instance, the accident investigation that eventually produced the NTSB’s very first AAR used data from a military air-defence radar to determine that a 727 that crashed into Lake Michigan had descended steadily into the water without levelling off, instead of suffering an uncontrolled excursion from level flight, while, more recently, primary returns received at several military radar sites in Massachusetts showed that EgyptAir Flight 990 pulled out of its initial dive before making a second and final plunge.
So what prevents civilian ATC radars from displaying altitude information for primary targets?

Also note that ATC uses more accurate altitude information than position information. If primary radar gives position to within 1/2 mile, that's good, but if it has the same accuracy for altitude, that's not good enough for separation.

because math...

Civilian Primary Surveillance Radar (PSR) does not provide elevation angle, and thus no altitude information can be displayed. The location is therefor not accurate either, but that doesn't matter for ATC purposes.
Civil ATC does not need altitude or height information to provide traffic separation when using PSR. They simple make sure the dots on the screen don't collide. For traffic separation you don't need to know the exact position of the aircraft; as long as the plots are separated on the 2D screen, the will be separated in the 3D world. Typical PSR displays are based on a flat world assumption; they only plot azimuth and range. As long as the plots are separated by 5NM, no matter what the altitude difference between the aircraft is, they are safely separated for ATC purposes.
As you correctly observed, if you would want to determine the exact 3D position of the aircraft based on a primary radar, you need azimuth, range and elevation angle. The PSRs used by civilian air traffic control don't measure the elevation angle, because this would require more sophisticated radar hardware and would therefore be more expensive.
The added value of the elevation angle is that the exact position including the height of the aircraft could be measured. However, that is of limited value. In air traffic control, vertical separation is not based on geometric altitude but on barometric altitude or flight level. Using elevation angle, the primary radar would give the geometric height. However, the barometric height showed in the cockpit to the pilot can easily be several hundreds or thousand feet off from the geometric height. So for the communication between ATC and pilots, geometric height measured by primary radar is mostly useless.
Aircraft are vertically separated by putting them on different altitudes/ flight levels, based on the baro altimeter in the aircraft. This altitude is transmitted to the secondary radar which allows display of that altitude and separation based on altitude difference. This is the basis for communication of vertical position information between ATC and pilots.
In short, the costs of adding elevation angle measurement to civilian primary ATC radar outweighs the benefits.

Aircraft are separated by putting them on different barometric altitudes/flight levels... above the transition altitude (usually 18 kft).  Which still leaves quite a lot of traffic below there...

@Sean I don't understand your comment. Below the transition altitude vertical separation is achieved by using different altitudes.

without knowing its elevation angle, it could be located anywhere along a circular arc extending from the horizon to the zenith at the specified distance from the radar

Well, not quite.  Aircraft are generally much more restricted in their vertical positioning.  If there's a return from 30 miles away, that aircraft can't be overhead.  (And radars normally have a maximum elevation to the beam, often around 70 degrees).
This document suggests that (at least as of 1989) determining elevation angle was very difficult for ATC primary radar.  It was possible by cross-correlating information from multiple feeds, but that this was not routinely done.  The document focuses on how useful that would be for helping to remove ground clutter.
Even if some elevation information were available, that data might not be presented to controllers unless it were of a useful precision.  If the precision were worse than say 1500 feet, would that be useful?

Besides, military radars can and do provide altitude information for primary targets

Radartutorial suggests that vertical discrimination (or 3D radar) requires extra equipment and is therefore more expensive.  Since ATC can get this information by secondary radar, the expense of gathering it via a 3D primary system is avoided.
Besides cost, older 3D radar would scan a region more slowly than a 2D radar.

Yes, I realise that aircraft have limits on how high they can fly, but a) different aircraft can fly at different heights, and b) that still leaves a large portion of the arc within the aircraft's flight envelope, so the general idea is still valid.

Primary (2D) ATC radar provides azimuth and slant distance but not elevation. If you use the slant distance as horizontal distance, it will be somewhat inaccurate, but since aircraft don't fly all that high (and shouldn't be above 10kft MSL at all without a working transponder), the error is minimal--and separation standards account for it.
Adding elevation scan (3D) would increase cost and slow scan rates yet add nothing when most aircraft have transponders anyway, so it's more efficient to live with the limitations.

Not all readers may realize that radar distance is diagonal without it being pointed out, and that is crucial to understanding it as a potential source of position error in the ATC context.

The limitations of ATC radar are simple: they are not designed to provide more than distance and heading for primary returns.
PAR (precision approach radar) is an example of a radar system which provides altitude information, and is configured to allow the controller to provide vertical approach guidance information.
There are many radar systems which provide elevation information, for example on some SAM (surface to air missile) systems.  It's possible, but someone has not spent the additional taxpayer funds for ATC purposes.

The new types on the market can do this.
See for instance Thales STAR-NG (altimetry option), Hensoldt (previously Airbus) ASR-NG, ...
You can also upgrade existing radars, such as the FAA ASR-9, as you can for instance see on the website of Intersoft.
There are however a number of limitations in performance, and more importantly, civil ATC procedures are not  designed to PSR derived altitudes. But even if not used operationally, it still provides a benefit in tracking and clutter rejection.


text:
Do takeoff (or other) performance calculations for jet aircraft take into account the type of fuel being used?
Jet aircraft can use any of a number of different fuels:1

Jet A-1 is a straight kerosene, not that much different from what you used to buy for committing arson fuelling portable space heaters.

JP-8 is Jet A-1 with the military’s stamp of approval.
Jet A, used almost exclusively in the United States (because ‘MURICA) and only available at a few non-US airports (most of them in Canada), is Jet A-1 with a slightly higher freezing point.2

Jet B is a mixture of 30% Jet A-1 and 70% unleaded gasoline, used in climates where Jet A-1 would freeze into a solid wax, due to its (Jet B’s) extremely low freezing point, and not (nowadays) used elsewhere, due to its extremely low flashpoint and high flame-spread speed.

JP-4 is Jet B with the military’s stamp of approval; it has now been retired from military service due to its excessive flammability and consequent handling difficulties, but is still included in the approved-fuels list for most jet engines, and, therefore, for the aircraft using said engines.

JP-5 is a high-flashpoint kerosene developed specifically for naval-aviation use, as an aircraft carrier at sea, unlike an airport or airbase on land, can’t easily call for mutual-aid support if things get out of hand, making it even more important to keep a fire from starting in the first place.
The Soviet Union had its own national jet fuels (both kerosenes, similar to Jet A-1, and cold-weather gasoline-kerosene blends [extra-important in places, like much of the former Soviet Union, that get really really cold in the winter], similar to Jet B), which can still be found in the former Soviet states, but are being gradually displaced by Jets A-1 and B.  China, like the former Soviet Union, has its own national jet fuels; China, unlike the former Soviet Union, still uses its own fuels essentially exclusively, making it especially important that anyone planning on fuelling a jet in China have it certified to burn Chinese jet fuel.

Different fuels presumably have different energy contents (the main split would be expected to be between the straight kerosenes [Jet A-1/JP-8, Jet A, JP-5, etc.] and the gasoline-kerosene blends [Jet B/JP-4, etc.], but there could also be smaller differences between the energy contents of the different fuels within each of these categories), which would affect the maximum power an engine burning one of these fuels would be able to produce, which would make a difference in terms of things like takeoff distance, allowable takeoff weight, and service ceiling for a given weight; is the type of fuel being used taken into consideration when doing performance calculations, or do the calculations simply assume the use of the least-energy-dense fuel in common use, or is there some other solution at play?

1: For that matter, a jet engine will happily run (for a while, at least) on essentially any combustible fluid that doesn’t produce refractory particles when burned (engines without moving turbine blades, such as ramjets, scramjets, and motorjets, don’t even have the refractory-particle limitation; neither do the afterburners of jet engines so equipped [same reason], if the afterburner is capable of drawing fuel from a different source than the engine core does), but most engine manufacturers never bother to get their engines certified to run on any of these exotic fuels, and many of them (the fuels, not the engine manufacturers) have other drawbacks that make them less suitable for aircraft-jet-engine use (for instance, bunker oil is excessively viscous and its freezing point is much too high, RP-1 is far too expensive for anyone not an Arabian oil sheikh, ethanol has a tendency to dissolve various important fuel-system components, diesel is OK in hot climates, but prone to freezing in the winter, avgas not only usually contains lead, which deposits on your sparkplugs3 and makes them less reliable, but is also far more of a fire hazard [due to its dangerously-low flashpoint and extremely high flame-spread speed] than jet fuel, and, on the other end of the flammability spectrum, JP-7 is so reluctant to ignite that the sparkplugs on most jet engines can’t reliably start it burning, with most jet engines designed to burn JP-7 instead using hypergolic ignition); ground-based gas-turbine engines, on the other hand, are immune to many of these drawbacks, as anyone with an M1 Abrams tank in their back garage can tell you.
2: There is technically a second difference; Jet A, unlike Jet A-1, is not required to include an antistatic additive, but most Jet A distros put it in anyways, as people tend to dislike having their plane blow up from a static discharge.
3: It does that to piston-engine sparkplugs, too, but this is tolerated for piston-engine use because the antiknock (or antidetonation, as many aircraft engine manufacturers insist you call it) qualities of avgas’s lead content let piston engines operate at much higher compression ratios - and, thus, much higher power settings - without the engine destroying itself; in contrast, jet engines, which are immune to knocking/detonation, derive no benefit from the lead, but still suffer from fouled sparkplugs due to it.

On the CF-34 family that powers most regional airliners, wide cut fuel is prohibited and there is no performance distinction between the various kerosene fuels, as the energy density effects are negligible.

@JohnK: Why are wide-cut fuels prohibited for the CF-34?  Do they damage the engine, or did General Electric simply never bother to get the engine certified to burn them?

Not quite sure why.  I believe because it burns a lot hotter and you would have to have a different fuel schedule and other complications that make it not worth it.  Possibly you can in the military version (It was originally developed for the A-10).  The PT-6 turboprop can run wide cut and can even run avgas and arctic diesel (near kerosene) for short periods.

For those not familiar with the term "wide cut fuel" (waves hand), I'll save you the search - read this answer.

In short, no.
Thrust is adjusted by engine pressure ratio and/or rotation speed. If physical output of the fuel is the same, it does not matter what fuel is burned.
If fuel causes other engine limits, for example exhaust or turbine temperature) to be reached before required thrust is achieved the takeoff is rejected.
The used fuel mostly affects cruise, because the fuel temperature is limited by its freezing point. During long cruise in high altitudes fuel in the wing tanks tends to get very cold. In such cases one would have to fly lower to warm up fuel which would have negative impact on fuel economy. Also, if I remember correctly King Air had an altitude and flight hour limitations (only to few hours) if widecut fuels were used.


text:
Why was a CFM56 conversion never offered for the short-body DC-8s?
A major part of why the DC-8 hung on well into the 21st century (albeit almost entirely in cargo service) was the late-1970s/1980s conversion of 110 DC-8-60s (out of a total of 262) into DC-8-70s; the main (or, for the DC-8-6/72 and DC-8-6/73, the only) change was the replacement of the DC-8-60's old, loud, thirsty Pratt & Whitney JT3D low-bypass turbofans, and the nacelles thereof, with new, [relatively] quiet, efficient General Electric/SNECMA CFM56 high-bypass turbofans (and the nacelles thereof).1 2
Only the DC-8-60 was eligible, though; the short-bodied versions of the DC-8 (the DC-8-10/20/30/40/50), which formed a slight majority of all DC-8s ever produced (2943 out of a total of 556, as compared to the 262 DC-8-60s)5 needed not apply, even though they would have benefitted just as much from the reengine as the DC-8-60 did, and the process would have been mostly the same (in fact, the DC-8-61 was merely a straight fuselage stretch of the last short-bodied version, the DC-8-55, and, yet, the former version got [the opportunity for]6 a reengine, while the latter did not).
Why did the short-bodied versions of the DC-8 never get offered the CFM56 upgrade that was extended to the DC-8-60?

1: Thus continuing a long tradition of up-engining older-model DC-8s to newer-version standard, although the DC-8-70 was the only DC-8 version for which this was the only possible way of getting one (without any being built new).
2: The April 1979 decision to reengine DC-8-60s with the CFM56, incidentally, saved said engine from extinction, allowing it (in multiple later versions) to later see service on the 737-300-through-900, A320ceo, and A340-200/300.
3: Over half of these were of the latest and greatest short-bodied DC-8, the DC-8-50 (142 built new, plus a total of 20 converted to DC-8-50 standard from DC-8-10s [12 aircraft], -30s [5], and -40s [3]); there were also 52 DC-8-30s (not including the five converted into DC-8-50s), and smaller numbers of -20s and -40s (but not -10s, all of which [except for two which crashed first] were converted to DC-8-20 or DC-8-50 standard).4
4: I am aware that many of the short-bodied DC-8s had either crashed or been retired by the time the 1980s rolled around; however, this was also true of many of the almost-as-old DC-8-60s.
5: Numbers from here (Wikipedia, unusually for it, has had some major inaccuracies regarding the production and conversion numbers for the short-bodied versions of the DC-8, especially the DC-8-50).
6: Surprisingly, many DC-8-60 owners and operators did not take the opportunity to upgrade their aircraft.  Out of 262 DC-8-60s produced, only 110 were reengined into DC-8-70s; some of the remaining 152 DC-8-60s were presumably aircraft that had already crashed or been retired by the time the reengine programme came around, but, even of the DC-8-60s that were still around, many went unupgraded.

I suspect it's because the business case just wasn't there. Every retrofit project I've been involved in boiled down to the money. Retrofits aren't cheap and ultimately the mods have to recoup those costs through improved revenue or decreased operating expenses.
Looking at your references, there was some structural changes to the wing and landing gear that came on the -55. I expect the earlier versions were ruled out of the mods due to the lack of those upgrades and the heavier CFM engines.
That doesn't explain why the -55 wasn't included. The Wiki article stated the -61 conversions did cost more than the -62 and -63 conversions because it had the shorter wing of the -55. So it boils down to the difference between the -55 and -61. Unmodified, the -61 had about 38% more payload capacity (72k lbs vs. 52k lbs). But the modified -71 lost almost 12k lbs of payload in the conversion due to the extra engine weight. So the -71 advantage over the -55 was only 20%.
The -72 and -73 didn't lose as much payload with the mods as they had the longer and stronger wing to start with. If you apply a weight penalty to the -55 similar to the -61 mods, it cuts the payload to approximately the same as the -43. That's about a 20% reduction in payload.
The other consideration is who was doing the mods.  I didn't do an exhaustive analysis, but the vast majority of the -7x conversions were for the big air cargo operators - Flying Tigers, UPS, and FedEx - or large leasing companies where the planes were in use in the US and Europe where noise was becoming an issue.
Many of the -6x aircraft that weren't converted (discounting those written off or broken up) were being operated in the countries where cheap trumps everything.
So most of the conversions were for cargo.  Another plus for the stretch aircraft is that cargo operations tend to max out on volume before weight. Obviously, that's not always the case, but the loads that max out weight tend to be special cargo (heavy equipment or machinery) not routine packages. The -71/-73 could carry almost 80% more volume than the short bodies.  Even the -72 had a 16% greater cargo volume. That's a big advantage in operational efficiency.
Since the long body could haul more cargo and generate a greater margin per flight, it made a worthwhile investment.

Great additions!

Going by the DC-8 production list linked in the OP, it looks like a lot of the DC-8-70s were converted for passenger airlines (mainly United and Delta, going by that list), and only later sold off.

United did have a number of -61s they converted to -71s and operated until about 1990. I expect the fuel savings and noise reduction let them keep them on line until they were able to replace them with B757/767 aircraft. The Delta -61s appear to have been converted just prior to their sale to UPS.

Pretty much.  That, and the four engines air carrier killed on by ETOPS capable twins.  Nobody wants to buy a DC-8 these days for cargo ops.


text:
Can 737NG GPWS and other warning voice lines/sounds be played in headphones instead of cockpit speaker?
I watched a couple of cockpit videos on the 737NG landing, and I noticed GPWS in some of the videos does not announce 500ft, 400ft, 300ft, etc. Does this mean the pilots have routed these sounds into the headphones, or they have been disabled on the particular operator’s aircraft?

No, the pilots cannot disable audio warnings or switch them over to headphones only. They are always send to the speakers and all headphones. The pilots cannot even adjust the volume for these warnings. This is to make sure that these warnings can always be heard regardless of any intentional or accidental misconfiguration of the audio control panel.

Audio warnings for altitude alert, ground proximity warning, collision avoidance,
  and windshear are also heard through the speakers and headsets at preset volumes.
  They cannot be controlled or turned off by the crew.

(Boeing 737 NG FCOMv2 5.20.1 - Communications - System Description)
The typical altitude callouts from the GPWS are:

Approach Callouts
Radio Altitude Callouts
[Option - Typical]
The GPWS provides the following altitude callouts during approach:

2,500 feet – TWENTY FIVE HUNDRED
1,000 feet – ONE THOUSAND
500 feet – FIVE HUNDRED
100 feet – ONE HUNDRED
50 feet – FIFTY
40 feet – FORTY
30 feet – THIRTY
20 feet – TWENTY
10 feet – TEN.

Note: Callouts at 1000 feet and 500 feet are based on barometric altitude above
  the landing field elevation; callouts at 2,500 feet, and below 500 feet are
  based on radio altitude.
DH/MDA Callouts
The GPWS provides height callouts based on the altitude set by the Captain’s Minimums selector.
Callouts are based on radio altitude when the MINS selector is set to RADIO. Callouts are based on barometric altitude when the MINS selector is set to BARO:

DH/MDA plus 100 feet – PLUS HUNDRED
at DH/MDA – MINIMUMS

(Boeing 737 NG FCOMv2 15.20.17 - Warning Systems - System Description)
All of these callouts are airline options and can be disabled by individual operators. There are also callouts at other altitudes, which are not listed here. See also Does the Boeing 737 NG have "5" radar altitude callout?.

Your first statement is a bit confusing saying "cannot disable audio warnings or switch them from speaker to headphones" which is true. But it should be made clear that you don't need to switch them to the headsets because they're already there; "also heard through the speakers and headsets at preset volumes."

@Gerry You're right, it was phrased a bit confusingly. I clarified it...

@Bianfable Why don’t you get “100 above”, here?

@cmp You do, I had just ended the quote before. I added the section to the answer now. I it "PLUS HUNDRED" in this FCOM, but some operators also use "HUNDRED ABOVE" or "APPROACHING MINIMUMS" instead.

@DigitalDracula Not that I'm aware of. Something like this is not mentioned in any Boeing FCOM I have access to.


text:
Is it possible to start another engine of Mil Mi 8 with one engine started and APU off?
In the 737NG, it is possible to start the other engine without APU if one engine is already started, by routing air from the started engine to the other one.
Is this possible in the Mil Mi 8 helicopter?

From that I see in the quite detailed description of the helicopter systems in Russian Wikipedia, looks like both engines have independent electric starters (starters-generators) so could be started independently.
There is no mentioning of APU in the description of all systems. They say power plant consists of the two engines. However as mentioned in comments, the helicopter does have the control panel for starting the "Турбоагрегат". It is generally a name for the device that combines turbine engine and electricity generator. APU is called "Вспомогательная силовая установка (ВСУ)" in Russian.

Mi-8 definitely has an APU.  You can see the relevant controls above the center of the windscreen, second panel from the bottom.  https://www.airliners.net/photo/Poland-Navy/Mil-Mi-17/2146005/L

While I can see a down vote for the incorrect assertion that the Mi8 doesn't have an APU, I'd say this deserves an up vote for answering the question by noting that it has electric starters and doesn't require the APU for either main engine start. Including the relevant Wiki quote (and a translation to English, even if it's a machine translation) is the expectation (links die and sources can get edited) would be worth another up vote (if only I had a 2nd to give).

I added comment about the existence of the ""Турбоагрегат".

From the linked article:  "Вертолёты поздних серий (Ми-8МТ, Ми-17 и др.) значительно модернизированы. Двигатели заменены на более мощные (взлётная мощность — 2200 л. с.) ТВ3-117 с 12-ступенчатым компрессором и воздушным запуском, для подачи воздуха к воздушным стартёрам двигателей установлена ВСУ АИ-9В."  The newer Mi-8s DO have APUs, and that's what the questioner is asking about.  This is not an answer to the question.

This sort of answers my question. Thank you, comrade!


text:
B737 during approach the G/s did not capture?
During a recent sim session this happened:
ILS radar vectors I armed the approach late initially the aircraft went left and right but it captured the LOC but the G/S was not captured.
Could someone please help me out?

What simulator?

737 NG Full motion simulator

You said you armed late, were you above GS when LOC captured?

Is this a commercial full motion simulato? Was the flight training or a checkride?

You were in a full motion simulator, which ain't cheap, so that indicates that you're already a commercial pilot, yet you're asking here on the internet, not one of your instructors? Hrm... Yet another airline to avoid...

Safety agencies recommend manufacturers to prevent the capture of the G/S by an aircraft not on the published glidepath (especially when close to the threshold), as explained in this question, with examples of serious incidents.

It sounds like you were high on the glideslope & getting higher by the time you got VOR/LOC capture. At that point, the GS typically won't capture unless you do something to get it centered again.
As a fix, if your procedures allow it, you could set a lower altitude such as localizer minimums into the MCP altitude window and then command a descent in Vertical Speed mode. That could get the GS centered, at which point the GS would capture, and you're back in business. It is entirely possible to capture the GS from above this way, but it has to be pretty well centered. If you're above it, the system won't dive down to capture it on its own.

Sounds like quite the stabilized approach?   Depending on how far out the GS is recaptured, it could be considered stabilized but it isn't starting out too well.

@wbeard52  Definitely not the ideal case, but in the sim, like the real world, such things can happen. If a bad vector from ATC means you capture the LOC slightly inside the FAF but you're 9 miles out at 3,000' above the runway, you have plenty of time to do what I described & you'll be stable well before 1,000'. If you're trying to sort this all out at a 1,400' GSIA, well, that gets more sporty. As a matter of kicking off the automation & hand flying it, if you're comfortable with that, it'd probably be the best bet, but if that's not comfortable... going around may be the best option.

I agree with you.  It is more important to be stabilized and there may be time to get stabilized by 1,000 FT AGL.  I don't necessarily think sim instructors do a great job of instilling ADM and wanting the crew to go-around when the approach becomes unstabilized due to time factors and the need to finish checking the boxes.

Hey yeah Ralph hit the nail on the head. you seemed to be above the glideslope and the aircraft was not able to change from "GS arm" (GS in white) to "GS active" (Green). A great way to get down is to use VS an put in about 1500-1800 to capture the GS. But be aware, it is poor form to have a VS that exceeds your altitude in AGL.


text:
What does it take from the airlines to be ETOPS certified?
I have been told that the airlines to be certified for ETOPS apart from the aircraft certification, engineering wise it should have some conditions met in order to get the certification and to maintain it too.

The requirements for ETOPS certification by the FAA are outlined in the following Advisory Circular:

ETOPS QUALIFICATIONS. The unique nature of ETOPS necessitates an evaluation of
  these operations to ensure that the certificate holder's proposed programs are effective. The FAA
  will review the certificate holder's documentation and training programs to validate that they are
  appropriate for ETOPS. To receive approval to conduct ETOPS the certificate holder must
  satisfy the following conditions:
a. Airplane. The specified airplane-engine combination listed in the certificate holder's
  application must have been certificated to the airworthiness standards of transport category
  airplanes and must be approved for ETOPS. Guidance for airplane ETOPS type design can be
  found in AC 25.1535-1 and § 121.162.
[...]
b. Flight Operations and Maintenance Requirements. The certificate holder must show
  compliance with the flight operations requirements discussed in paragraph 303 and the
  maintenance requirements discussed in paragraph 301.
c. Training Requirements. The certificate holder should show that it has trained its
  personnel to achieve competency in ETOPS and must show compliance with the flight
  operations and maintenance training requirements discussed in paragraphs 302 and 304.
d. Requirements For ETOPS Approval. Before the FAA grants ETOPS operational
  approval to an applicant for two-engine ETOPS, the certificate holder must be able to
  demonstrate the ability to achieve and maintain the level of propulsion system reliability that is
  required for the ETOPS-approved airplane-engine combination to be used (appendix P to
  part 121, section I, paragraph (a)). The certificate holder must also demonstrate that it can
  operate the particular airframe and other airplane systems at levels of reliability appropriate for
  the intended operation. This can be achieved directly by a successful in-service operational
  history or by successfully validating all the required ETOPS processes according to the
  Accelerated ETOPS Application Method in Appendix 3 of this AC.
e. Accelerated ETOPS Application. An applicant for an initial operating certificate who
  is applying for ETOPS authority at entry into service under the Accelerated ETOPS Application
  method must comply with the same requirements for certificate holders outlined in this AC. It
  should be understood that validation of an applicant with no previous operational experience
  should be more robust than would be necessary for a certificate holder with operational experience. As is the case for all Accelerated ETOPS approvals, the Director, Flight Standards
  Service must be satisfied that the applicant can operate to the standards expected of an
  experienced ETOPS operator from the first day of service.

(FAA AC-120-42B)
The referenced paragraphs 301 to 304 can be found in the same document and provide detailed requirements for operations, maintenance and training.
The details may vary around the world, but other aviation authorities will have similar requirements for certification.


text:
Could a moving film of gas reduce aerodynamic drag?
Source: Wikipedia
In this image there is depicted a system which creates, using the Coandă effect, a film of gas traveling along the surface of a body. If this object was moving through air in the "up" direction on the image, could aerodynamic drag be reduced since the gas at the boundary layer of the body would have lower velocity than the free stream air (in relation to the body)?

Related: Will it reduce lift in proportion?

No, it doesn't reduce drag through reducing boundary layer speed, but it does create thrust by creating a region of low pressure in front of the vehicle (I mean technically, if the entire vehicle produces thrust, it does reduce vehicle drag, but in either case the reason why that happens isn't because the boundary layer speed is reduced). If you mount the device like in the image, then the low pressure zone will be created. The pressure at the bottom of the vehicle is higher than on the top, so it will generate forward thrust (well, in the orientation of the image, upwards thrust). This is because a jet of fluid will entrain it's surrounding fluid (aka "pull the fluid along with the jet"), which will create a region of low pressure around the jet. There actually are real-life implementations of this concept -

,

.
However, the reason why this isn't used in real life is because if it's low efficiency - there's other ways to generate that thrust, such as using a propeller, a turbofan engine, etc, that don't require nearly as much fuel to produce the same thrust.

Only if you somehow manage to reduce friction. This could be achieved by using a gas with a significantly lower viscosity than air. As long as a sufficiently thick film is maintained, it will produce lower shear stress than an air boundary layer would while maintaining flow speed at its outside, so the air flowing around the object will not be subjected to shear.
While hydrogen has less than half the viscosity of air, its low density will make it disappear quickly (on the other hand, the needed mass of hydrogen per volume is unbeatable). A mixture of propane and ethane looks promising to me, but I cannot remember to have ever seen experimental evidence for the feasibility of this concept.
A similar concept is used by fish which are covered in a slimy film which reduces friction with water. Also, the supercavitating torpedoes successfully use a film of gas bubbles to reduce friction. So I see no obvious reason why your idea would not work. However, the gas needed to be carried along will eat into the possible payload, so this looks most promising for short range.

For the system to reduce drag, it has to eject air faster than the speed of flight. Much slower and it looks to the oncoming air like a wider body and that tends to increase drag, counteracting any low-pressure effect.
Coanda's original idea was to use a similar system to create thrust by inducing a flow of ambient air alongside. He built a plane to demonstrate the effect in 1910. Although it failed to generate the anticipated thrust, it has gone down in history as the first jet plane ever built.
Placing the exit half way back along the surface to re-energise the boundary layer after it has slowed down is less demanding on the exit velocity, but it requires a high volume of air. Such blown wings have been tried and it does work, but the complexity, weight, bulk and cost of the system mean it is not worth doing.

You think of rocket-like thrust generation. The question clearly does not: "the gas at the boundary layer of the body would have lower velocity".

@PeterKämpf The question title bears slightly wider explanation, in my humble opinion.


text:
Can I fly through these military airfields' class C airspace?

I am a low time private pilot now based in Pensacola. I’m a bit unsure how the Class C of PNS/NAS Whiting Field is handled. As you can see they all overlap. PNS is a civilian field while the others are military. If I was going to fly VFR to the northeast, can I fly through the Class C of Whiting field? I always get flight following when departing.

North Whiting Field and South Whiting Field are training bases with a fairly high density of student flight training going on; North is fixed wing, South is helicopters.  Is it your intention to to fly through that airspace without talking to anyone?  Do you always make sure to squawk 1200 and have your transponder on?  Your intentions are unclear in asking this question: what's really the problem to solve here?

There are some general answers to questions like this, but you might also want to sit down with a local CFI and discuss it. In most areas there's a lot of 'local knowledge' on airspace and procedures that you won't find in any chart or document. Especially in that location with a lot of military traffic, special use airspace and a special rules area.

Thanks for the replies. My concern was the legality of departing PNS and entering adjacent class C after being told to “maintain VFR” as departure usually says.  I fly a 150 so climbing above the top of the Class C takes time.

When entering Class C Airspace:
Since all the airfields are Class C you would need to contact the approach control prior to entering.  Approach control should be able to direct you appropriately from there.  Approach control would handle traffic at all three airports. If the military airfield does not want civilian aircraft to cross the field for any reason approach control will direct you around it.  If there is nothing going on at the military field then approach control could let you cross over the field.
When Departing Pensacola Field:
When departing Pensacola field you can request a Northeast departure through Clearance Delivery.  You could be granted the request to fly Northeast directly from the airport or they could make you fly East for a while then make a turn North to avoid the military airport.  Nevertheless you have to follow ATCs instructions whenever you are in Class C airspace.
Side Note:
It is fairly common that when you have military airfield close to a Class C airport, the class C airspace will be extended over the military fields as well so that one approach control would handle all the traffic and deconflict traffic for all of the fields.  A similar situation exists for the Tucson area where the Class C includes Tucson International and Davis Monthan AFB.

If I was going to fly VFR to the northeast can I fly through the
  Class C of Whiting field?

As long as you contact the NDZ tower/approach control and they respond to your call you are cleared through the Class C as you would be through any class C.
However also to the northeast you will find R-2915A and the Eglin base area which has some special rules. The FAA offers a nice course/overview on it you can find here.
Generally speaking you are allowed to fly close to military bases and into their airspace so long as that airspace is not prohibited or a hot restricted area.

I think you would need to talk to approach control, not tower.  FYI, there are two towers... one for the North field and one for the South field.  But, I see they are the same freq...

When departing KPNS (or any class B/C), you'll call Clearance Delivery before taxi and tell them which direction you want to depart, and they'll give you a squawk code and (maybe) what heading and altitude to fly immediately after takeoff.  Then you call Ground to taxi as usual.
After takeoff, KPNS Tower will hand you off to Departure, who will likely give you a new heading and/or altitude once you're on radar.  Ideally, you'll have climbed above the other Towers' airspace within a few miles and thus can stay with Departure the entire way out.  If your climb performance sucks, they may turn you to avoid a handoff, or they might have a local agreement that lets them handle you anyway, e.g. if you're just going to clip a corner on the way up.
The key point is that as long as you're talking to ATC, they'll hand you off to whoever controls wherever you're headed next without you having to worry (much) about who that may be ahead of time.  All those complicated lines are mostly just for folks trying to fly without talking to ATC.

You're never allowed into class B or C without appropriate communication.  Contact approach, and ask them to enter the airspace.  If they clear you in, then you can.  If they tell you to remain clear, then the answer is no.
I don't know why everyone wants to make every answer into an editorial.

Welcome to ASE! Long answers that explain things in detail, including sources and citations, is the purpose of this site.  Your answer has some not-quite-correct information.  Class C does not require "clearance" to enter. It only requires positive communication be established.  If you contact approach and they say your call sign, you're allowed to enter. "Cessna 123AB, standby", and you can go in, even though they didn't "clear you in".

I've edited my answer in an effort to be more pedantic.  If a long explanation with references is necessary, then I get it.  Sometimes all of that is simply not necessary.    the question was "can I fly through the Class C".  The answer is just as simple as the question.

That's true, but the actual underlying question is much more complex than just "can I?", with in a simple, "yes you can" answer. The questioner states that s/he is low-time, and specifically mentions being "unsure of how it works", since there are multiple/stacked Class Cs and one of them is around a military field.  An "editorial" answer is definitely called for to help the questioner go from "rote knowledge" to a deeper understanding of the process and procedures.  (I'm not trying to be a dick... you stated you don't know why, and I'm just explaining why)

Class C doesn't need a clearance, two-way radio communications is sufficient

Steve Kuo - unless that two-way communication includes "remain outside class Charlie". Right? Or does that qualify as "two-way communication", and therefore you can enter without "clearance"?

User36228 - You are correct, if you are told to remain clear of class Charlie, you have to remain clear. However, even if they told you to "stand by" you can now enter class charlie as that constitutes two-way radio communication.


text:
Why is the missed-approach course for the "RNAV (GNSS) - A" approach to runway 28 at ENSB shaped all funny?
Svalbard-Longyear (ENSB) has one particular approach (the RNAV (GNSS) - A approach to runway 28) whose missed-approach course is... oddly-shaped, to say the least:

(PDF by Avinor; screenshot and cropped by me.)
If the pilots can't see the runway by the time they reach SB709, they have to make a right-angle turn to the left just before reaching SB705, followed by a series of three right turns that end up with the aircraft aimed at NAXEN and its holding pattern (and flying directly over the substantial mountains immediately to the north of Adventfjorden en route).
The hockey-stick-shaped missed-approach course can't be for obstacle clearance, given that all this manoeuvring is carried out over the water - indeed, the other two approaches to runway 28 (the unadorned RNAV (GNSS) approach and the localiser approach) have missed-approach courses which each include but a single, wide, conventional turn en route to the holding patterns at the NAXEN waypoint and the Longyear NDB, respectively - so why does this particular approach have such a weird missed-approach course?

My guess would be to allow time to climb over terrain. On the regular RNAV you would go missed above 1400 ft. But on this app you could go missed at 650 ft and would need time to climb over the 3000 ft terrain.

As Alexander already said in his answer, the turns over water are executed to gain enough altitude before turning back over the terrain.

(left: RNAV-A, right: RNAV approach chart).
The difference between the RNAV-A approach and the other two (RNAV and LOC) is the required minimum climb gradients for these two approaches. You find them at the bottom of the approach charts (percent values before the *) for the latter two:

(RNAV)

(LOC)
The OCA (Obstacle Clearance Altitude) is different depending on the missed approach climb gradient (and approach category), thus ensuring enough terrain clearance with the normal turn to NAXEN (RNAV) or LON (LOC).
The RNAV-A approach does not list a minimum approach climb gradient and can therefore be flown by aircraft with a lower climb performance, which requires more track over water before turning back, hence the funny shape. Note however, that the approach chart says

CAT A, B only.

for the RNAV-A, so it is limited to aircraft with a maximum reference speed of 120 kt.

If you look at satellite imagery it looks like you have very high terrain to the west of the runway. The water would be the primary area available for a climb back to obstacle clearance altitude. Looks like the MAP just routes you with sufficient time to climb to the MA altitude.

(Google Maps)


text:
EOSID - Adhere to at or soon after V1?
Most airports have an Engine Out Standard Instrument Departure (EOSID) statement similar to this on their charts:

For EOSIDs, the take-off performance for "ABC Airport" is based on the following Engine Failure Procedure and routes. They must be adhered to, at or soon after V1. Maintain between 15-25 bank angle and a maximum of 190kts IAS during turns.

My question is:
Is the V1 catered for balanced or unbalanced field length, and how does it affect obstacle clearance?

Care to define "EOSID" for those not familiar? (Some people aren't pilots and are just here to learn.) Also, I presume "ABC Airport" is a generic place. Please improve the formatting of your opening paragraph to make it more readable, you can quote a block of text using the > character at the beginning of a line of quoted text, or put it in quotes "" or something to help improve readability.

Thank you FreeMan! I will update the question with your recommendations!

Thanks. I tweaked the formatting a bit to try to make it a bit smoother

V1 should be calculated based on the actual conditions, so if you have an unbalanced field available, that's what it should be calculated from.
The V1 speed itself has zero effect on obstacle clearance. In most cases, V1 can be selected within a range between the lowest accelerate-go speed and the highest accelerate-stop speed, and that selection in & of itself won't change how much you clear any obstacles in a given scenario, unless the V1 was high enough to keep you on the ground.
Obstacle clearance is affected by things like rotation point and speed, climb speed, and thrust available. If the choice of V1 has effects on these, then there may be secondary effects, such as those coming from ruling out cases with a very late & very slow rotation (i.e. a high V1 means that early engine failures result in an abort rather than a continued takeoff).
A high V1 means that the worst case that you have to consider starts with more energy, having had all engines working for longer during the takeoff roll. But, if the engine were to fail at any point other than that worst case, how far past V1 you are makes no difference.

Thank you for the explanation Ralph J! So if the choice of V1 has no effect on obstacle clearance, since the OPT (on-board performance tool) would have catered for it... would there be any benefit in delaying my rotation past Vr (rotate speed) during an engine out? I am thinking no, because doing that will affect my ability to achieve 35ft above the end of runway.

Well... I'm not going to advise anybody to operate outside of their written procedures, so this isn't a recommendation for that.  There can be advantages to a later, faster rotation speed, if the available runway permits. The computed performance data is based on rotating at Vr in all cases (unless they give you something else, like SETOS -- the "Single Engine Take Off Speed", which the T-38 had).  If you're taking off from a 12,000' runway in something reasonably light, delaying rotation by a few knots probably doesn't reduce your runway end height below 35', but without data...

... without data specific to your conditions & runway, you don't really know how close you are to a performance limit, and if that extra 10 knots will cause a problem somewhere else.  There could be cases where a published SETOS well above Vr might do good things for your climb performance later, but if you don't have that data, I wouldn't go making it up on the fly.  (That said, rotation rates engine-out are often a bit slower than normal, and that's often written in the procedures... which has a bit of the same effects as an increased Vr.)


text:
Why is there bronze powder aboard blimps to be used as pyrotechnics?
I'm reading the airship pilot manual for the Goodyear K-Type blimps and in the table of "Empty Weight", at page 18 under the heading "Pyrotechnics", there are listed "24 Bronze Powder Markers" for a total weight of 48 lb.
Googlin' I just found references to makeup stuff and artists' colors, but those applications don't fit under the heading "Pyrotechnics"...
Can anyone shed light?

Curiously - both bronze/brass and aluminium were scarce resources in WW2, but more-so for the central powers and Japanese.

Although the Japanese captured the major supplier of tin at the time (Malaysia), they did not have a domestic copper supply. However, the US and allies had to deal with (re)finding tin supplies. My grandfather, a mining engineer, spent WW2 in the Andes evaluating all the old mines for reopening to supply tin (and copper).

Bronze powder drift signals could be dropped on the ocean surface as a marker.
It seems most likely that there was not any pyrotechnic element to the powder - that is, it didn't burn on the surface in any way. The patent for the Surface Marking Signal (1944) - basically a bomb-shaped object to be dropped from an aircraft - provides the best description of how bronze powder was used as a marker. The powder

provides for the marking of a continuous, homogeneous, and visible
spot on the surface below... to provide a marking on the surface such
as open water... to mark the location of a previous seen object.
The invention consists of a a powder contained in a streamlined shell.
The shell is such that on striking water... it will break and release
the powder... The powder is of a composition which will spread into a
single homogeneous visible spot when it is released on the surface...
suitable materials are pale gold bronze powder and sodium  fluorescein
salt.

source
In the United States Official History of the Sea Search Attack Group (1942 - 1944) there is a description the crew of a Douglas B-18 Bolo  carrying out an anti-submarine attack:

As there were oil slicks astern of the submarine to approximately
mark its position, no bronze powder signal smoke or smoke flare was
dropped.

It's a bit ambiguous: I imagine it would work quite well sitting on the surface of the water and glittering if the conditions were right. However, if we take "bronze powder signal smoke" to be a single phrase, then it indicates that there was some airborne element to the bronze powder, rather than just being a passive marker.
Another WW2 document entitled INSTRUCTIONS FOR COORDINATED EFFORT OF DESTROYERS AND PLANES
AGAINST ENEMY SUBMARINES says:

Planes of the Inner Air Patrol may drop aluminum or bronze powder
bombs to mark suspected contacts, for their own benefit in making
further investigation.

while Naval Aviation News of October 1943 warns:

bronze powder spilled from a drift signal container caused serious
corrosion to the bottom of a seaplane due to galvanic action with
aluminum and salt water... extreme care should be exercised in
handling bronze powder drift signals.

Aluminium Bronze Powder was also used as to add to the coating of aircraft, but this is not what it was for in your manual.

source

"I imagine it would work quite well sitting on the surface of the water and glittering if the conditions were right. " I imagined the same before posting my question, I figured a sort of rocket that blasts the bronze powder on the sea surface, but mine it's just imagination…

"Aluminum Bronze Powder". Make up my mind, is it aluminum or bronze???

@FreeMan Aluminum Bronze - it's a bronze (copper alloy) made with aluminum instead of tin.

thanks, @R.M. Confusing just on the face of it...

The patent is 1944, the manual is 09/1942, revised 09/1943 (indicated in the right bottom of the front page), Nevertheless, I think you're very close to a definitive answer.

And recall that tin production centered on Malaysia pre-WW2, so the Japanese invasion cut off that source of tin. Anything that could be made with something other than tin moved to that alloy to save tin for shells.

@gboffi  I don't see an issue with those dates - the patent is for something that uses "Bronze Powder" so we should expect the powder to have been invented some time earlier.

In addition, WWII practice bombs were filled with metal powder to produce an easily-visible splash mark when they struck the ground, so the bombardier could see how close he got to the intended target.


text:
Weird seat numbering on Boeing 737-800
I recently flew in a Boeing 737-800 in Thailand.
My seat was 53K so I thought: "That's a big plane for such small domestic travel."
When I entered the plane however I discovered that seats start at number 31, so 53 was actually the 22nd row instead of the 53rd.
But even stranger was that the letters on one side were A,B,C but on the other side were H,J,K (not only skipping several letters but not even consecutive letters).
The plane was a standard middle corridor with 3 seats in each side.
Is there any logic in numbering seats like this?

Welcome to Av.SE.  This question may be a better fit on Travel.SE, since they're more focused on the "passenger" side of things, while this forum is more focused on the "pilot" side.  That said, let's see if you get a good answer here before having a moderator migrate the question.

This is a good question and answerable but i feel it more belongs to travel.se

I would imagine this is related to having a common factor across all fleet types, eg I would imagine that Economy class across all aircraft types, both Narrow and Widebody, start at 31.
Similarly if you booked an 'A' or 'K' seat you would be assured of a window, or a 'C' / 'D' seat would always be an aisle in the window block.
HJK is not consecutive because I and O are generally unused where they can be confused with the numbers 1 and 0(zero).

Makes sense. Thanks


text:
If calculating turbulence is computationally expensive, why not do something simpler?
I understand that people use the RANS/LES equations to calculate how air flows above a wing. But what is the exact formula that people use to derive coefficients like drag / lift after doing these calculations?
Do people do these calculations just to look at pretty pictures?
Is fully simulating turbulence overkill if you're just trying to get 2 coefficients (lift / drag) for a wing?

Your title question seems to have little to do with the question body. Care to [edit] to make them line up?

Thank you for the suggestion!

They still don't (to me) seem to be asking the same thing, but maybe I just don't understand what you're after.

You're correct, most CFD is overkill.  Most engineers are not taught when a tool is overkill -- they're just taught to use the 'best' tool they have.
CFD produces pretty pictures that can give insight into a flow -- which can sometimes help diagnose and fix problems with the flow.  Beyond that, it often boils down to a smaller set of numbers that are calculated.  As you pointed out, lift and drag coefficients are two important ones.  CFD will calculate all six major coefficients -- three forces and three moments.  All six are worth having.  CFD can also calculate the load distribution across the wing, which is important to feed over to the structures folks.  Of course, these things can be calculated with much simpler methods.
Most aircraft operate at quite high Reynolds numbers.  The boundary layers are relatively thin, and the pressure distribution around the aircraft can be treated as inviscid.  A panel code, or even a vortex lattice calculation will do a good job at estimating the six forces and moments (and load distributions) except for viscous contributions to drag, stall, and transonic effects.  An Euler code will be able to handle transonic effects and other complexities of compressible flow.
Basic viscous drag can be estimated with a wetted area / form factor buildup.  This won't tell you details of where problems occur, but it will get you a very close approximation of the cruise drag.
All of these are approximations, a good engineer understands them and uses good judgement to know when to use which tool.  CFD is not only an approximation because of the mesh resolution and the simplification of turbulence.  But most CFD geometry models leave out a lot of details of the aircraft -- finite trailing edge angles, gaps and seams, fasteners, antennae and other protuberances, flap tracks, control surface hinges, bonding straps, etc. etc.  To capture these things, the geometry model would be much more complex, the meshing effort would surely double, the mesh size would probably double, and the computation time would increase accordingly.
Most CFD is run with control surfaces un-deflected.  This means the aircraft is not trimmed in pitch.  Most CFD is run without propulsion effects of the engines -- the aircraft is not trimmed in Thrust/Drag and the effect of the giant vacuum cleaner is ignored.
To get around these limitations, you need to run a bunch of CFD cases -- say at a bunch of angles of attack and with a few control surface deflections.  Then, you can do some offline calculations to approximate what the drag of the trimmed solution would be if you were to run it.  Likewise, you end up doing a handbook base drag buildup to add in the drag of all the things you left out of the CFD model.
That is just for an ordinary cruising aircraft.  For complex models like an eVTOL aircraft with many rotors that possibly tilt as it goes through transition -- trim is a complex 6DOF problem and there are many redundant control effectors.  You're interested in many angles of attack and climb angles at many velocities through transition.  This flow is inherently unsteady and CFD calculations take a very long time.  In the end, a single CFD solution is nearly useless -- to get something useful, you need hundreds of such solutions.
Again, this is where lower fidelity tools (some of which can trim on the fly) really shine.
There are times when CFD is essential, but often it is over-used.  Master the spectrum of tools and you'll be way ahead.

It seems to me that fully simulating turbulence is overkill

For a modern jetliner one can expect its boundary layer to be turbulent on 90 to 95% of its surface. Due to the lower Reynolds numbers, that range can be better for a GA airplane made of smooth carbon fiber - but the most part of its surface is going to have a turbulent boundary layer too.
Being able to simulate turbulence is therefore of paramount importance in order to calculate with confidence the aerodynamic characteristics of the airplane.

what is the exact formula that people use to derive coefficients like drag / lift after doing these calculations?

It's enough to use the definition of those coefficients:
$\begin{cases}
C_l=\frac{L}{½ \rho V² S}\\
C_d=\frac{D}{½ \rho V² S}\\
C_m=\frac{M}{½ \rho V² Sc}
\end{cases}$

Oh, so if my CFD simulation gives me density and velocity of a unit of air (assume 5cm x 5cm x 5cm) above a section of the wing, I can calculate $C_l$ provided by that unit by plugging in $S = 5cm^2$ and the projection of the velocity component onto the wing's surface (to get the value for V that I need to plug into the formula for $C_l$)? Then I just sum up all the contributions of $C_l$ from all the units of air above the wing to get the total lift provided by the wing?

If that is the case, can't we just run 100 steps of CFD to get the average $\bar{Cl}$ and say: "this wing gives us $\bar{Cl}$ amount of lift for this angle of attack and incoming wind speed"?

Density, wing surface and speed are known quantities which you define and are not calculated by the CFD. The CFD returns the total aerodynamic forces acting on your airplane. Then you take, say, the vertical component of this forces, you call it lift $L$ and you use the definition to get the relevant $C_l$. Afterward you run another CFD simulation with slightly different conditions, you get a new $L$, you calculate the relevant $C_l$ and you can compare it with the previous one to see if the new conditions get you a better airplane.

You are greatly overestimating the non-turbulent parts of the flow on jetliners. Wing sweep and nose devices force turbulent transition on the wing and on the fuselage practically all surface has a turbulent boundary layer. Laminar flow will not extend much beyond the radome.

@PeterKämpf: that's why I wrote that the turbulent part can be as high as 100% of the surface. I don't get your comment...

@sophit It would be better to give a range of 95% to 100%. Due to their much lower Reynolds numbers, GA airplanes have more laminar flow. The way you write it gives the opposite impression.

@PeterKämpf I'll rephrase it then

Fully simulating turbulence around a whole aircraft is overkill. It is also impossible for real-word Reynolds numbers for any foreseeable future even on supercomputers. You mention LES (large eddy simulation) and RANS (Reynolds-averaged Navier-Stokes). Neither fully simulates turbulence.
In RANS, all turbulence is modeled by approximate models, no turbulence is simulated.
In LES, the large turbulent structures are simulated, but due to the necessity to use affordable computational grids, the small structures are modeled by approximate models.
In turbulent flow, the turbulence also affects the mean flow, through the presence of the turbulent stresses in the Reynolds-averaged Navier-Stokes equations. Therefore often, you have to somehow simulate the effects of turbulence, at least by modelling the turbulence by approximate models in RANS, to get the right flow shape, and especially flow separation.
In nice attached flow, you can often get away with Euler equations or even by potential flow. That does NOT mean that CFD is overkill! Both of these approaches ARE CFD, if they are used for a numerical simulation on a computer on a grid (but analytical computations of Joukowski profiles using conformal conformal projection with a pen and paper or anything similar with other equations is not CFD). Even the small disturbance potential equation simulations are still CFD.
When flow separates, it is often necessary to model (or simulate, if you can afford it) turbulence as precisely as possible to get the flow shape and the Reynolds number dependence right. Getting reasonable computational result for a lift coefficient is quite easy. What is much harder is a good result for the drag coefficient. Especially the skin friction contribution is tricky and requires resolving the boundary layers well even for attached flow.
Also do not forget that an airplane is not just the wing but also other structures, where the flow is much more complicated and harder to compute with analytical methods.

What is the exact formula for the lift and drag coefficients? Another answer gives you their definitions. But that is really just scaling to different dimensionless units.
The main point you have to do is to compute those forces!
To compute the forces you need to extract tje forces caused by the pressure distribution along the body and the forces caused by viscous friction along the body. You have to integrate those across the whole surface. The pressure force is perpendicular to the surface and the viscous force is parallel to the surface in the direction of the local flow speed.
The more difficult one, as already mentioned, are the viscous forces (skin friction). You need properly resolved boundary layers including the viscous sublayers. Just using the a wall function with the law of the wall in some form will cause significant inaccuracies.

You are correct that Euler solvers are CFD.  However, most people do not consider potential flow solvers -- VLM, Panel codes, LLT, etc. to be CFD.  In practice, the difference usually involves whether a volume mesh is required.  In terms of pure definition, I think the difference has to do with whether you are solving the differential equations directly (vs. an algebraic superposition of solutions as in potential flow methods).  By either of these definitions, full potential solvers and transonic small disturbance would both be CFD.